A study published today in PNAS shows that reading a backlit device before bed makes your sleep measurably worse than reading a paper book under dim light.

According to the study:

• While people are using an iPad at night their body produces 55% less melatonin
• After shutting off the lights (and the iPad), they took an extra 10 minutes to fall asleep
• When they did fall asleep, they had less REM sleep during the night
• The next morning, the iPad readers felt sleepier, and it took them “hours longer” to feel alert. The book readers quickly felt more alert immediately upon waking.
• When it was time for bed the next night, the iPad readers’ circadian clocks were delayed by more than 90 minutes. Their bodies began to feel tired an hour and a half later than normal, because they were exposed to alerting light from the iPad the night before.

Each participant was tested with both the iPad and reading a book. Books on paper did not suppress melatonin or cause participants to feel groggy the next day.

The 5-day study was conducted by Anne-Marie Chang, Daniel Aeschbach, Jeanne F. Duffy, and Charles A. Czeisler at Brigham and Women’s Hospital (a Harvard Medical School teaching hospital).

f.lux’s take

This study shows that the bright blue light from displays at night is impacting our sleep. If you stay up late reading a bright iPad until just before bedtime, your sleep will be negatively affected, and your body will expect to stay up later the next night (as much as 90 minutes later). You may have trouble winding down, feeling alert when you should be getting tired.

This level of melatonin suppression is quite large. Melatonin is known as the sleep hormone, and has many functions in the body related to sleep. It is also a strong anti-inflammatory known to suppress cancer cell growth.

Because the circadian shift of using an iPad at night is very large, only a few nights of staying up late reading might put your body several hours out of phase with your normal routine.

Click here to read our suggestions on how to safely use screens near bedtime.